如图，函数y=f（x）在区间[a，b]上，则阴影部分的面积S为（   ）

A：${\displaystyle \int {}_a^b}$  f（x）dx

B：${\displaystyle \int {}_a^c}$  f（x）dx﹣ ${\displaystyle \int {}_c^b}$ f（x）dx

C：﹣ ${\displaystyle \int {}_a^c}$  f（x）dx﹣ ${\displaystyle \int {}_c^b}$ f（x）dx

D：﹣ ${\displaystyle \int {}_a^c}$  f（x）dx+ ${\displaystyle \int {}_c^b}$ f（x）dx